1. Field of the Invention
The present invention is directed generally to a radiant energy based target acquisition and tracking seeker for a missile or munition projectile of a class of such ballistic projectiles and, more particularly, to an improved seeker system which incorporates an uncooled, infrared-sensitive, two-dimensional focal plane detector array in conjunction with signal processing electronics. The focal plane detector array accomplishes high resolution target imaging and is capable of operation in a staring mode.
2. Related Art
It is known to incorporate various types of radiation sensitive systems into the nose cones of guided missiles and other types of ballistic projectiles for use in target acquisition, tracking and homing. Some of these systems employ radiant energy detecting multiple targets of interest and/or discriminating between a plurality of targets of interest having different energy levels or spectral characteristics.
One such system which utilizes a vidicon to obtain a video image as a second order discriminant and as a source of guidance data in conjunction with an infrared (IR) hotspot detection technique is illustrated and described in U.S. Pat. No. 4 615 496 to Pinson. That system uses a central processing unit (CPU) to compare vidicon generated images with predefined stored criteria based on size, temperature and distribution of multispectral characteristics. Tracking data based on the target positioned in the field of view (FOV) are used to fly the missile to the target. The system uses an infrared seeker to first detect hotspots in the field of view prior to video data processing which is used to image a selected field of view based on the detection of an hotspot. The hotspot is indicated by infrared energy levels above a preselected established threshold at a known frequency.
A further hotspot detecting radiation tracking apparatus is shown in U.S. Pat. No. 3 944 167 to Figler, et al. That system uses multiple electro-optic arrays to define inner and outer fields of view, together with IR bandpass filters, to discriminate between true and false targets.
While such devices have met with some degree of success, they all require mechanical rotating filter and/or chopping devices to permit rapid alternate exposure of the sensing system to incoming radiation and background for comparison. This limits their application to relatively low acceleration ("low g") environments such as launched ballistic missiles or the like. Most have IR systems that require cryogenic cooling to operate. The need for precision mechanization and cryogenic cooling add undesirable cost to the device. In addition, imaging resolution quality is generally less than desirable for proper target discrimination except in very high cost systems.
Infrared detection devices of high accuracy have traditionally been composed of materials such as mercury cadmium telluride (Hg(.sub.1-x) Cd.sub.x Te) which have operated at cryogenic temperatures and thus have always required complicated cooling systems. Recently, however, arrays of very small, sensitive bolometer devices capable of detecting infrared (IR) and millimeter or microwave (mm) energy have been developed which are capable of operating at ambient temperatures. Such an array, in the form of a monolithic integrated focal plane array, which is sensitive to several wavelength ranges of interest is exemplified by the disclosure of U.S. Pat. No. 4 654 622 to Foss, et al.
Such devices have heretofore not been adapted for use in the missile or projectile target acquisition and homing systems. The so-called silicon microbridge sensors, however, are solid-state in nature and do not require cryogenic cooling; and, it has been discovered that these arrays do not require alternating comparison exposure and so can be used in a staring mode. This eliminates the need for an intermittent shutter (chopper) or rotating filter device. These advantages, together with the solid-state nature of sensors made from microbridge arrays, indicate that they can be subjected to extremely high g forces without harm.
Recently, very compact, biaxially pivoting gimbal mounting systems for carrying and directing the field of view of radiation sensitive seeking devices have also been developed. One such device, known as an "eyeball" gimbal is described in U.S. Pat. No. 4 490 724 to Bickman. That system discloses an arrangement in which the drive and measurement components for both the outer gimbal and the inner gimbal are mounted on the frame. This provides maximum space within the gimbals for a sensor, simplifies the determination of the inner gimbal angulation and allows compact operation with respect to inner and outer gimbal rings.
It is also known to digitize a stream of analog pixel array data, or the like, and process it into very high resolution digital images within a field of view. Representative techniques are illustrated and described in U.S. Pat. No. 4 220 972 to Geokezas, et al., U.S. Pat. No. 4 519 041 to Fant, et al., and U.S. Pat. No. 4 561 104 to Martin.
Much research has been carried out in an effort to make such systems more versatile and able to stand more adversity in launch and flight and yet reduce the cost of such systems to thereby reduce the cost of fired projectiles. However, there remains a need for a low-cost, versatile, high resolution target acquisition seeking system for projectiles capable of operating in a very high g environment.